ok so im about to install my hot water shower.alittle confused though.can i connect the hot water from the thermastat housing or the plug on the intake manifold?i was going to go off the block underneath but there seems to be some tubing coming out to something.i think i see were for the cold water,aft the seawater pump.dont know if the ca models are diffrent but mine already t off into some other peice,not sure what it is.here is a pic of my themastat housing,can i use any of these outlets for the hot water?

Your #1 plug would work fine for your cold water supply.
I just put a 1 1/4" double barbed by thread Tee on the output hose of the impeller pump. Just cut the hose stick the barbed Tee in there and use that as your cold water supply.
Your hot water supply will be on either side of the block, centered about 2" above the oil pan.
There should be a brass 3/8" plug, or there may be some insturmentation plugged in there, so check both sides.

on my block i sont have just the plug,it comes out to some other tubing and runs into something else,think it must be some sort of smog stuff since im in ca.
another guy told me he ran his hot water off the #1 plug and has no problems

FYI I installed a hot water shower on my boat and initially used the drain plug underneath the manifolds for my hot side. I had nothing but troubles with clogging. Once I used the intake plug side it worked flawlessly. Mine was not where your's is though, its on the manifold itself I believe.

tested this weekend and works great,used the #1 on the thermastat housing.only problem i have is i tied into hose after the seawater pump for cold water.i installed a flojet ondemand pump,when the motor is off there is still hot water but because the impeller blocks off the cold water flow its just hot water.i might have to plumb into it before the pump.